Cross-bridge-dependent Changes in the Intracellular Ca2+ Concentration in Mammalian Cardiac Muscles.

A change in muscle length significantly alters the developed tension in mammalian cardiac muscle compared to that in skeletal muscle fibers. The intracellular mechanisms related to the length-dependent change in developed tension have been studied using Ca2+ indicators in intact preparations; a cross-bridge-dependent change in the affinity of troponin-C for Ca2+ is a possible mechanism. This hypothesis is further supported by the measurement of Ca2+ bound to troponin-C in skinned preparations. The molecular mechanism of the cross-bridge-dependent change in the affinity of troponin-C for Ca2+ is not fully understood although the studies which employ the substitution of troponin-C in skinned preparations, transgenic animals and in an animal model with heart disease have been performed. We reviewed the current studies by analyzing the intracellular mechanism responsible for the length-dependent change in tension development in mammalian cardiac muscle.